The present invention relates to an internal-combustion engine with a direct fuel injection device.
More particularly, it relates to a direct-injection internal-combustion engine comprising at least a cylinder, a cylinder head, a piston sliding in this cylinder, intake means for at least one gaseous fluid, a multijet fuel-injection nozzle comprising a fuel jet angle and a fuel jet nappe angle, and a combustion chamber delimited on one side by the upper face of the piston comprising a teat pointing towards the cylinder head and arranged in a concave bowl.
In the case of Diesel engines working in homogeneous mode, it is well-known to mix the fuel coming from a multijet injection nozzle with the gaseous fluid(s) admitted into the combustion chamber of this engine, such as air or a mixture of recirculated exhaust gas (EGR) and air, so as to obtain a homogeneous fuel mixture before combustion starts.
This fuel mixture homogeneity allows to reduce the consumption and to minimize the production of nitrogen oxides (NOx) and of particles.
In order to favour mixing of the fuel with the gaseous fluid admitted in the combustion chamber, engines comprising injection nozzles with a large number of holes, of the order of 20, have been developed.
This injection nozzle type allows to improve the running conditions of the engine in homogeneous combustion mode, but it leads to wetting of the cylinder wall by the fuel droplets, notably when the inner aerodynamics of the combustion chamber uses a swirling motion of the gaseous fluid admitted, which throws these droplets onto this wall.
This wetting of the wall by the fuel does not only lead to a degradation of the behaviour of the lubricant present on this wall and to the creation of soots, but also to an emissions increase and to a decrease in the engine performance, notably by increasing its fuel consumption.
In cases where this engine works under conventional combustion conditions, notably at high loads so as to reach a high torque and a high specific power, such a number of jets is not compatible with this combustion mode.
In fact, when the axes of the fuel jets are circumferentially too close to one another, the ends of these jets overlap each other in the bowl, thus preventing mixing with the gaseous fluid and creating too fuel-rich zones, which leads to the formation of soots.
The present invention is aimed to overcome the aforementioned drawbacks by means of an engine of simple and economical design.
This engine can run in two combustion modes, the change from one to the other being carried out essentially by shifting the injection phases.
The geometry selected for the jets is based on the use of an injection nozzle of small nappe angle associated with a particular number of jets so as to, on the one hand, provide sufficiently homogeneous mixing of the fuel with the gaseous fluid(s) admitted (air or recirculated exhaust gas and air) while preventing wetting of the cylinder wall by the fuel in homogeneous combustion mode and, on the other hand, to provide good independence of each fuel jet in conventional combustion.
The invention therefore relates to a direct-injection internal-combustion engine comprising at least a cylinder, a cylinder head, a piston sliding in this cylinder, intake means for at least one gaseous fluid, a multijet fuel-injection nozzle comprising a fuel jet angle and a fuel jet nappe angle, and a combustion chamber delimited on one side by the upper face of the piston, said face comprising a teat pointing towards the cylinder head and arranged in a concave bowl, characterized in that the fuel jet angle is at least equal to             10      ⁢              xe2x80x83            ⁢      π        FD    ,
where FD is the diameter of the bowl bottom, and the nappe angle is less than or equal to       2    ⁢          xe2x80x83        ⁢    Arctg    ⁢          CD              2        ⁢        F              ,
where CD is the diameter of the cylinder and F is the distance between the point of origin of the fuel jets and the position of the piston corresponding to a crankshaft angle of 50xc2x0 in relation to the top dead center.
Preferably, the fuel jet nappe angle can be less than or equal to 120xc2x0.
Advantageously, the nappe angle can range between 40xc2x0 and 100xc2x0.
The angle at the vertex of the teat can be selected greater than the nappe angle by a value ranging between 0xc2x0 and 30xc2x0.
The axes of the fuel jets can form an angle of intersection of the order of 5xc2x0 with the flank of the teat.